Moses Farrow, the adopted son of Woody Allen and Mia Farrow, posted a 4,600-word essay on Wednesday defending his father against sexual molestation allegations and claiming his mother was abusive.

In the blog post, titled “A Son Speaks Out,” Mr. Farrow, 40, described repeated spankings by his mother and other abuse, and what he called “a deep and persistent darkness within the Farrow family.”

He recalled, too, his version of the events on Aug. 4, 1992, when his sister, Dylan Farrow, then 7, claimed Mr. Allen, one of the most prolific directors in modern cinema, sexually molested her at their home in Bridgewater, Conn. Moses was 14.

On Thursday night, Mia Farrow said that her estranged son’s claims were “completely made up.”

And Dylan Farrow, now 32, responded to the essay in a tweet, writing that her brother sought to “impugn my mother who has only ever been supportive of me and my siblings.”

She called his comments hurtful and an attempt to discredit her. “I’m so sorry he’s doing this,” she wrote.

This is not the first time Moses Farrow has supported his father in an acrimonious family battle that has pitted mother, father, brothers and sisters against one another in a very public scrum. In his essay, he said he decided to speak out again now, hoping people will be more receptive to his story.

His mother acted in more than a dozen of Mr. Allen’s films while they were together from 1979 to 1992, although they lived in separate Manhattan apartments on opposite sides of Central Park.

They split after she discovered nude photographs Mr. Allen had taken of Soon-Yi Previn, then 22, the daughter she had adopted while married to André Previn, the pianist and conductor.

Mr. Allen and Ms. Previn married in 1997 and have two adopted children.

In “Start to Finish: Woody Allen and the Art of Moviemaking,” a book published last year by the author Eric Lax, Moses Farrow said his mother was abusive and had coached his sister to accuse Mr. Allen of sexual abuse.

In his essay, Mr. Farrow, who is a family therapist, claimed that his mother spanked and slapped him, and sought to brainwash him and his siblings to keep them under her control. In all, Ms. Farrow oversaw a brood of 14 children. Ten were adopted. (Three of her adopted children are deceased.)

“In short, it was not a happy home — or a healthy one,” he wrote.

The comments about his sister, Dylan, are the most provocative. In the essay, he questioned his sister’s account of sexual molestation, writing that her memory was faulty. For example, he wrote that an electric train set she described seeing was not kept in the attic, where she said she was assaulted, but in a brother’s room. Further, he wrote, there were too many people around not to notice something was amiss.

Also in recent years, her brother Ronan, who was 4 at the time of the allegations, has spoken out about her case, while reporting on sexual misconduct by Harvey Weinstein and other powerful men for The New Yorker, work that shared a Pulitzer Prize with The Times this year. With greater attention on harassment and sexual misconduct from the #MeToo movement, many in Hollywood have said they would not work with Mr. Allen again.

In his statement on Twitter, the journalist said his brother’s essay was part of a “repeated campaign to discredit my sister, often by attacking our mother.”

He continued, “My mother did an extraordinary job raising us, and none of my siblings with whom I’ve spoken ever witnessed anything but love and care from a single mom who went through hell to keep her kids safe.”

In a brief interview over direct message on Twitter, Mia Farrow said Thursday that Moses had cut off all ties with the family years ago.

“I guess I should be used to these attacks after 20 years,” she said. “But still, using my son as a weapon is new and excruciating. Also, it’s still flabbergasting that he can tell so many lies when the facts are readily available.” She said they are clearly listed in court documents from the original investigation.

That 1993 investigation into Dylan Farrow’s allegations took several turns. She was interviewed nine times, and the doctor who headed the investigation, John M. Leventhal, said there were inconsistencies in her account. That same year, Ms. Farrow was awarded custody of her three children with Mr. Allen. Months later, a Connecticut state attorney declined to prosecute Mr. Allen despite “probable cause” on charges of sexual molestation.

The decision was made to spare Dylan Farrow additional trauma, the prosecutor said, with agreement from her mother.

Patrick LaForge contributed reporting.

A version of this article appears in print on , on Page A13 of the New York edition with the headline: Three Farrows Dispute a Son’s Defense of Woody Allen. Order Reprints | Today’s Paper | Subscribe